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Blood
Blood
• The only fluid tissue in the human body
• Classified as a connective tissue
• Components of blood
– Living cells
• Formed elements
– Non-living matrix
• Plasma
If blood is centrifuged…
• Erythrocytes sink to the bottom
(45 percent of blood, a percentage
known as the hematocrit)
• Buffy coat contains leukocytes and
platelets (less than 1 percent of
blood)
– Buffy coat is a thin, whitish layer
between the erythrocytes and plasma
• Plasma rises to the top (55 percent of blood)
Hematocrit
• Measure of percentage of red blood cells in
the blood
• Normal hematocrit ranges from 37-45%
• Low hematocrit could indicate anemia
(anemia means “lacking blood”)
– Can indicate disease or blood loss
• High hematocrit (polycythemia) can cause the
blood to become thick and form clots
Physical Characteristics of Blood
• Color range
– Oxygen-rich blood is scarlet red
– Oxygen-poor blood is dull red
• pH must remain between 7.35–7.45
• Blood temperature is slightly higher than body
temperature at 100.4°F
• In a healthy man, blood volume is about 5–6
liters or about 6 quarts
• Blood makes up 8 percent of body weight
Plasma
• Composed of approximately 90 percent water
• Includes many dissolved substances
– Nutrients
– Salts (electrolytes)
– Respiratory gases
– Hormones
– Plasma proteins
• Most made by liver
• Incudes clotting proteins
– Waste products
Formed Elements
• Erythrocytes
– Red blood cells (RBCs)
• Leukocytes
– White blood cells (WBCs)
• Platelets
– Cell fragments
Erythrocytes (Red blood cells or RBC)
• Main function is to carry oxygen
• Anatomy of circulating erythrocytes
• Biconcave disks
• Essentially bags of hemoglobin
• Anucleate (no nucleus)
• Contain very few organelles
• 5 million RBCs per cubic millimeter of blood
Hemoglobin
• Iron-containing protein
• Binds strongly, but reversibly, to oxygen
• Each hemoglobin molecule has four oxygen
binding sites
• Each erythrocyte has 250 million hemoglobin
molecules
• Normal blood contains 12–18 g of hemoglobin
per 100 mL blood
Leukocytes (white blood cells or WBCs)
• Crucial in the body’s defense against disease
• These are complete cells, with a nucleus and
organelles
• Can move by amoeboid motion
• Can respond to chemicals released by
damaged tissues
• 4,800 to 10,800 WBC per cubic millimeter of
blood
Abnormal numbers of leukocytes
• Leukocytosis
– WBC count above 11,000 leukocytes/mm3
– Generally indicates an infection
• Leukopenia
– Abnormally low leukocyte level
– Commonly caused by certain drugs such as
corticosteroids and anticancer agents
• Leukemia
– Bone marrow becomes cancerous, turns out excess
WBC
Platelets
• Derived from ruptured multinucleate cells
(megakaryocytes)
• Needed for the clotting process
• Platelet count ranges from 150,000 to 400,000
per cubic millimeter of blood
– 300,000 is considered a normal number of
platelets per cubic millimeter of blood
Hematopoiesis
• Blood cell formation
• Occurs in red bone marrow
• All blood cells are derived from a common
stem cell (hemocytoblast)
• Hemocytoblast differentiation
– Lymphoid stem cell produces lymphocytes
– Myeloid stem cell produces all other formed
elements
Formation of Erythrocytes
• Unable to divide, grow, or synthesize proteins
• Wear out in 100 to 120 days
• When worn out, RBCs are eliminated by
phagocytes in the spleen or liver
• Lost cells are replaced by division of
hemocytoblasts in the red bone marrow
Control of erythrocyte production
• Rate is controlled by a hormone
(erythropoietin)
• Kidneys produce most erythropoietin as a
response to reduced oxygen levels in the
blood
• Homeostasis is maintained by negative
feedback from blood oxygen levels
Formation of WBCs and Platelets
• Controlled by hormones
– Colony stimulating factors (CSFs) and interleukins
prompt bone marrow to generate leukocytes
– Thrombopoietin stimulates production of platelets
Hemostasis
• Stoppage of bleeding resulting from a break in
a blood vessel
• Hemostasis involves three phases
– Vascular spasms
– Platelet plug formation
– Coagulation (blood clotting)
Step 1: Vascular spasms
Step 2: Platelet Plug Formation
Step 3: Coagulation
Hemostasis
• Blood usually clots within 3 to 6 minutes
• The clot remains as endothelium regenerates
• The clot is broken down after tissue repair
Undesirable clotting
• Thrombus
– A clot in an unbroken blood vessel
– Can be deadly in areas like the heart
• Embolus
– A thrombus that breaks away and floats freely in
the bloodstream
– Can later clog vessels in critical areas such as the
brain
Bleeding Disorders
• Thrombocytopenia
– Platelet deficiency
– Even normal movements can cause bleeding from
small blood vessels that require platelets for
clotting
• Hemophilia
– Hereditary bleeding disorder
– Normal clotting factors are missing
Blood Groups and Transfusions
• Large losses of blood have serious
consequences
– Loss of 15 to 30 percent causes weakness
– Loss of over 30 percent causes shock, which can
be fatal
• Transfusions are the only way to replace blood
quickly
• Transfused blood must be of the same blood
group
Human Blood Groups
• Blood contains genetically determined
proteins
• Antigens (a substance the body recognizes as
foreign) may be attacked by the immune
system (A and B antigens)
• Antibodies are the “recognizers”
• Blood is “typed” by using antibodies that will
cause blood with certain proteins to clump
(agglutination)
Blood Group
RBC Antigens
Plasma antibodies
Blood that can be
received
AB
A, B
None
A, B, AB, O
Universal recipient
B
B
Anti-A
B, O
A
A
Anti-B
A, O
O
None
Anti-A, Anti-B
O
Universal donor
Rh Blood Groups
• Named because of the presence or absence of
one of eight Rh antigens (agglutinogen D) that
was originally defined in Rhesus monkeys
• Most Americans are Rh+ (Rh positive)
• Problems can occur in mixing Rh+ blood into a
body with Rh– (Rh negative) blood
Rh Dangers During Pregnancy
• Danger occurs only when the mother is Rh– and
the father is Rh+, and the child inherits the Rh+
factor
• RhoGAM shot can prevent buildup of
anti-Rh+ antibodies in mother’s blood
• The mismatch of an Rh– mother carrying an Rh+
baby can cause problems for the unborn child
– The first pregnancy usually proceeds without
problems
– The immune system is sensitized after the first
pregnancy
– In a second pregnancy, the mother’s immune system
produces antibodies to attack the Rh+ blood
(hemolytic disease of the newborn)
Blood Typing
• Blood samples are mixed with anti-A and
anti-B serum
• Coagulation or no coagulation leads to
determining blood type
• Typing for ABO and Rh factors is done in the
same manner
• Cross matching—testing for agglutination of
donor RBCs by the recipient’s serum, and vice
versa